The Ministry of Justice guidance says guards should use the formal address for at least 12,000 prisoners with learning difficulties such as dyslexia.

The guidelines have been issued after Kenneth Clarke, the Justice Secretary, attacked as “ridiculous” a ruling that forced guards to call a notorious gang boss serving life for murder “Mr”.

One senior prison officer last night dismissed the guidelines as “unnecessary” and there were more important issues to deal with than what a prisoner is called.

The 26-page Ministry of Justice document called ‘Ensuring Equality’ states that prison workers have a ‘moral duty’ to ensure fairness to all.

It lists a string of “minority groups” which are singled out for special treatment, including elderly, disabled, gay, transsexuals, religious groups.

It says that when dealing with prisoners with learning disabilities, they should “use the prisoner’s name at the start of each sentence”.

They should also “prepare the prisoner for each stage of the communication – for example ‘Mr Jones, I am now going to ask you some simple questions’, or ‘Mr Jones, I am now going to explain what we are going to do’.”

The Prison Service Instruction (PSI) states that prison officials are not in a position to tell a prisoner if they think they have learning difficulties, adding: “If a prisoner does not think they have learning disabilities, it is not for staff to inform them otherwise.”

Inmates with dyslexia would be classed as having learning difficulties and it is believed they could be at least 12,000 prisoners in that situation.

Steve Bostock, national vice-chairman of the Prison Officers Association, said: “I do not see what difference calling someone with dyslexia Mister is going to make.

“These guidelines are pretty unnecessary and there are more important things to be worrying about that calling someone Mister.”

A prison source, who did not want to be named, said: “We have long been aware of the importance put on equality for prisoners, but for officers to have to address prisoners by their name at the start of every sentence is taking things too far.

“The prison service has changed for the better in the past 10-15 years, but there are some aspects of these orders which really stick in out throats, and this is one of them.”

Last year Colin Gunn, who is serving at least 35 years for orchestrating the murder of an innocent couple as a “revenge” attack on their son, won the right to be called Mister.

He complained that staff did not abide by unwritten rules that inmates should be addressed by their preferred title and won the backing of the prisons watchdog, leaving staff with little option but to address him as “Mr Gunn”.

At the time, Mr Clarke described the case as an example of “ridiculous” human rights claims “by ridiculous people”.

A Ministry of Justice spokeswoman said last night insisted there was no general order call all prisoners Mister.

She said the guidelines refers “specifically to those prisoners who self-report as having learning difficulties” to ensure “all prisoners, with reasonable adjustment, have access to all aspects of prison life”.